In recent years, a demand for an optical transmission system corresponding to 40 gigabits per second (Gbps) or 100 Gbps has been increased. As realization means for the optical transmission system, the adoption of various modulation systems superior in frequency use efficiency, noise immunity, and the like is searched for. In particular, a multi-level modulation system with which multi-bit information is transmitted in one symbol time (time interval to transmit a modulated signal) attracts attention. For example, reviews on a system of combining multi-level modulation and polarization multiplex, a system of performing multi-level quadrature amplitude modulation through the combination of the phase and the amplitude, and the like are actively carried out.
In optical transmission system adopting the above-mentioned multi-level modulation system, depending on an operational environment of the system such as a state of a transmission line, a signal to be decoded on the reception side may be received in a different state from an original signal modulated on a transmission side in some cases. For this reason, a situation is known in which logic inversion and replacement of transmitted bits are generated in one symbol time, and the transmission data may not be normally received.
As a technology for detecting the above-mentioned logic inversion and replacement to perform the compensation, for example, Japanese Laid-open Patent Publication No. 2009-89194 discloses an optical transmission system based on a multi-level modulation system using the polarization multiplex in which bits for detection having a particular pattern set in accordance with the number of bits transmitted in one symbol time is assigned to a transmission signal, an optical signal modulated in accordance with the transmission signal is transmitted from an optical transmitter, and in an optical receiver, by using the bits for detection contained in the reception signal, the logic inversion or bit swap (replacement of bits) of the reception data is detected to perform the compensation.
Also, as a related technology for performing respective processings for the above-mentioned the transmission signal and the reception signal at a high speed, a technology is known in which data stored in a frame is rearranged in a plurality of logical lanes, and a signal processing is carried out in the respective the logical lanes. With regard to this frame rearrangement, for example, U.S. Pat. No. 7,362,779 discloses a method of rearranging data while rotating the logical lanes when the data in a plurality of frames is rearranged in the respective logical lanes.